Expanded metal is used for various purposes, e.g. to fill containers for combustible liquids or gases, in particular fuel, to prevent explosion-like combustions. In general, the expanded metal used for these purposes is made from very thin aluminum foil of a strength of about 40 .mu.m.
Apparatus for providing such expanded metal generally make use of knives arranged transversely to the conveying direction of the foil so as to provide small cuts transverse to the conveying direction. Stretching of the foil is obtained by operating the discharge unit of the apparatus at a speed higher than the speed of the feed unit so that the foil is stretched in the conveying direction.
The expanded metal obtained in such a manner has only limited dimensional stability so that the filling with such expanded metal of, e.g. automobile gasoline tanks, balls up after a short period resulting in a loss of its explosion-preventing property.
It has therefore been proposed to produce expanded metal from thicker aluminum foils, e.g. with a thickness of 0.65 to 0.85 mm. However, as it has turned out, the above-described apparatus could not be used with such aluminum foils as their strength was too high to provide an expansion in longitudinal direction of the foil provided with transverse cuts simply by increasing the discharge speed relative to the supply speed.
From the German patent No. 749 689 an apparatus for cutting off wire-like strips from a foil is known in which a cutting unit includes a stationary knife edge and a knife which is designed as a milling cutter and is provided with cutting edges. The continuous cuts as provided by the unit extend perpendicular to the conveying direction of the foil.
The British Pat. No. 1 590 636 discloses an apparatus for profiling metal foils including a pair of rollers having a spacing from each other which is smaller than the thickness of the foil to be profiled. In addition, the rollers have a length which is smaller than the width of the foil so that a partial expansion of the foil is obtained in longitudinal direction during its passage through the pair of rollers. Arranged downstream of the apparatus is a further pair of profiled rollers which provides a profile transverse to the longitudinal direction of the foil in the respective expanded area.